This invention relates to an apparatus for measuring such physical quantities as temperature, humidity and velocity, to a method of manufacturing the apparatus, and to a method of writing correlative data into the apparatus.
A conventional digital thermometer, as previously disclosed in Japanese Patent Application Laid-Open No. 131576/75 and illustrated in FIG. 1, has a non-volatile storage element mounted thereon. In this example of the prior art, the non-volatile storage element stores correlation data, between temperature and the output value of a counter circuit, which is obtained in advance and then written into the non-volatile storage element. However, since a digital thermometer of this type is not equipped with an input/output unit for creating or for writing the correlation data, such data must be written into the non-volatile storage element off-line, and it is difficult to put the non-volatile storage element into the form of a large-scale integrated circuit together with the other principal circuit portions. Furthermore, since the sensing circuit used in writing the correlation data differs from the sensing circuit of the device on which the non-volatile storage section is mounted, it is difficult to create correlation data which is not influenced by the variance or dispersion in the electrical characteristics of the sensing circuit components. Lastly, the fact the correlation data is written into the non-volatile storage element off-line requires that the correlation data be so managed as not to mix with other data. Such management of data in the course of the writing process is complicated and requires particular care.
With the measuring apparatus as shown in FIG. 2, since the correlation characteristics between a physical quantity and the electrical parameters of a sensor are generally non-linear, a converting circuit (bridge circuit) is added to the sensor, thereby providing a linear output, in order to simplify the circuit which executes the subsequent signal processing. In addition, though there is a variance in the correlation characteristics between a physical quantity and the electrical parameters of separate sensors, the correlation characteristic can be standardized. This may be accomplished by using the variable resistors VR.sub.1, VR.sub.2, shown in FIG. 2, to regulate both the zero point and the amplitude of the linearized output of the bridge circuit, thereby standardizing the characteristic. Nevertheless, this method involves complex circuitry and a troublesome adjustment operation.